High-order elliptically polarized harmonic generation in extended molecules with ultrashort intense bichromatic circularly polarized laser pulses

Abstract

Numerical solutions of the time-dependent Schr\odinger equation (TDSE) for a two-dimensional ${\mathrm{H}}_{2}{}^{+}$ molecule excited by a bichromatic ultrashort intense circularly polarized laser pulse with frequencies ${\ensuremath{\omega}}_{0}$ and $2{\ensuremath{\omega}}_{0}$ and relative carrier envelope phase $\ensuremath{\phi}$ are used to explore the generation of high-order elliptically polarized harmonics as a function of internuclear distance $R$. Optimal values of $\ensuremath{\phi}$ and $R$ for efficient and maximum molecular high-order harmonic generation (MHOHG) are determined from a classical model of collision with neighboring ions and confirmed from the TDSE nonperturbative simulations. Maximum elliptically polarized harmonic energies of ${I}_{p}+13.5{U}_{p}$ are found, where ${I}_{p}$ is the ionization potential and ${U}_{p}={I}_{0}/4{m}_{e}{\ensuremath{\omega}}_{0}^{2}$ is the ponderomotive energy at intensity ${I}_{0}$ and frequency ${\ensuremath{\omega}}_{0}$. The polarization properties of MHOHG, phase difference $\ensuremath{\delta}$, ellipticity $\ensuremath{\varepsilon}$, and orientation angle $\ensuremath{\varphi}$ are presented as well. The high efficiency of the proposed MHOHG scheme should be useful for production of elliptically polarized attosecond extreme ultraviolet pulses.